High strength,heat resistant fluoroelastomers



United States Patent 3,438,932 HIGH STRENGTH, HEAT RESISTANT FLUOROELASTOMERS Jerry K. Sieron, Dayton, Ohio, assignor to the United States of America as represented by the Secretary of the Air Force No Drawing. Filed Dec. 9, 1966, Ser. No. 600,669 Int. Cl. C08f 29/16, 45/04 US. Cl. 260-41 2 Claims ABSTRACT OF THE DISCLOSURE This invention encompasses reinforced fluoroelastomer materials suitable for seals, O-rings, clamping devices, etc., which have high tensile strength, high tear, high heat resistance, good compression set and utility at 700 F. for reasonable time periods. In particular the invention concerns a vinylidene fiuoride-perfluoroethylene copolymer vulcanizate containing acicular-platy talc as a reinforcing material.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

This invention deals with elastomeric materials suitable for seals, O-rings, tires, clamping devices, and the like, said materials having high tensile strength, high tear strength, high heat resistance, good compression set, and being suitable for use at temperatures as high as 700 F. for reasonable time periods. More particularly, the invention deals with a fluoroelastomer vulcanizate reinforced with the acicular-platy form of magnesium silicate.

Subsystem components of advanced aerospace systems are being subjected to ever increasing environmental requirements. Notwithstanding any advance in this art to date, considerable advantage will be gained by the discovery of higher strength and higher heat resistant elastomer compositions for use in tires, seals, hoses, clamping devices, and the like. Research to date in this art has involved the study of reinforcement, stabilization, and improved cross linking of fluoroelastomers and other polymers.

It was found, for example, that the use of compositions comprising hydrocarbon elastomers reinforced with fine particle size, high structure carbon black was a decided advance in the art. Also, the use of stannous oxide as a stabilizer for phenolic resin cured butyl elastomers provided a composition effective up to temperatures of 500 F. Further, butyl-ethylene-propylene terpolymer vulcanization-stabilization systems have been developed which extend, 3-fold, the useful life of the terpolymer at temperatures in the range 300500 F. Another noteworthy advance in the art resulted from the use of fiuoroelastomers reinforced with carbon fibers. The latter composition has good high temperature tensile strength and improved life at temperatures up to 600 F.

OBJECTS It is an object of my invention to provide improved high strength, high heat resistant fluoroelastomer compositions with good compression strength.

It is a further object to provide such compositions wherein a unique reinforcing agent imparts improved tensile strength, improved hot tear strength, and improved resistance to deterioration in the temperature range 600- 700 F.

I have now found that the foregoing and related objects can be attained with a composition comprising a fluoroelastomer reinforced with acicular-platy (A-P) magnesium silicate which is a particular form of mineral talc.

My novel compositions are mixed and molded (or otherwise formed) by the methods commonly practiced in the art. I generally mix a fluoroelastomer with a filler such as magnesium oxide, the reinforcing agent of the invention, and a vulcanizing agent such as an alicyclic amine salt or benzoyl peroxide. The composition may then be molded into an O-ring, for example. The product is commonly press-cured at about 330 F. for 30 minutes and is then post-cured by raising the temperature to 400 F. over a period of 4 hours and holding at 400 F. for 24 hours.

Any fiuoroelastomer may be used in the composition; e.g., polymers and copolymers of vinylidene fluoride, perfluoropropylene, chlorotrifluoroethylene, and the like.

Asbestos, also a fibrous form of magnesium silicate, has been used as a reinforcing agent for fluoroelastomers and it produces a good tensile strength product. However, the use of asbestos leads to severe degradation when the vulcanizates are subjected to aging at 600 F. Various forms of carbon such as MT Black and fibrous carbon (for example, as sold under the trade name Carbon Wool), have been used with some success and these materials have been used as controls in evaluating the value of acicular platy magnesium silicate as a reinforcing agent (see Tables 1, 2, 3, and 6).

The acicular-platy magnesium silicate can be used over a wide range of concentrations relative to the fluoroelastomer. However, I recommend that 1050 parts, and preferably about 30-40 parts, of reinforcing agent per 100 parts elastomer be used (see Table 4).

The compositions of the invention have good compression set (generally about 40 percent) and have a 400 F. tensile strength which is percent greater than that attainable with the commonly used thermal carbon black reinforcing. When hot tear strengths are compared, my novel compositions show up even better. In addition to the value of these properties in seals, gaskets, flexible connectors, coated fabrics, and the like; I have found the compositions to be especially suitable for dynamic seals, such as rotating rod seals, because fibrous talc of the acicular-platy type is inherently non-abrasive, thus imparting low wear characteristics to seals.

EXAMPLE A number of elastomer compositions were prepared. These comprised the copolymer of vinylidene fluoride and perfluoropropylene parts by weight), and alicyclic amine salt curing agent (2 parts), magnesium oxide (15 parts), and a reinforcing agent. Table 1 shows the formula used. The formula used in the tests reported in Tables 26, inclusive, is the same except that the reinforcing agent is changed as indicated in each table.

Table 1 shows the comparison between MT carbon black and acicular-platy magnesium silicate (referred to as A-P talc).

Table 2 shows a comparison among 3 types of magnesium silicate-asbestos, powdered, and the acicular-platy form.

Table 3 shows the comparative effect of 600 F. aging on compositions containing MT Black, Carbon Wool, and acicular-platy magnesium silicate.

Table 4 shows the effect of varying the concentration of the reinforcing agent of the invention.

Table 5 shows the comparative effect of 700 F. aging on compositions containing MT Black, Carbon Wool, and talc.

Table 6 shows the comparative tear strength of compositions aged at 400 F.

It is to be understood that the foregoing example and description are for the purposes of illustration only, and

that various changes may be made therein without depart- TABLE 3 mg from the Spll'lt and scope of the invention.

1 Reinforcing Agent TABLE 1 Mt. Carbon A-P [Press-cure: 30 min/330 F.; Post-oil 4 hrs. rise to 400 F.+24 hrs/400 5 Black Wool Tale Original at 75 F.: Formula Control A-P Talc Tensile Strength, p.s.i- 2, 460 1,980 2, 400 Elongation, percent-.. 275 195 240 Elastomer 100 100 Hardness, Shore A, pa 75 78 75 Magnesium Oxide 15 15 Original at 400 F.! Medium Thermal Carbon Blac 30 Tensile Strength, p.s.i.-... 340 590 610 A-P Talc 20 Elongation, percent 100 110 Alioyclic amine salt 2 2 Aged 24 hr./600 F., Tested at 75 PHYSICAL PROPERTIES- rlglna at 75 Tensile Strength, p.s.i 1, 490 1, 980 F.: Elongation, percent 135 150 Tensile Strength p.s.i 2, 460 2, 400 Hardness, Shore A, parts.. 82 82 Elongation, percent 275 240 Aged 48 hr./600 F., Tested at 75 F. Hardness, Shore A 75 75 Tensile Strength, p.s.i. 750 1,170 1,720 Original at 400 F.: Elongation, percent 150 110 125 Tensile Strength, p.s.i 340 610 Hardness, Shore A, parts... 81 8'1 86 Elongation, percent 105 110 Aged 72 hr./600 F., Tested at 75 F Aged 72 hrs/600 F., tested at 75 F Tensile Strength, p.s.i 1 490 1,130 1, 220 Tensile Strength, p.s.i 1 490 1, 220 Elongation, percent.-. 80 120 80 Elongation, percent 80 80 Hardness, Shore A, parts 9O 88 87 Hardness, Shore A 90 87 Aged 96 hr./600 F., Tested at 75 F Aged 16 hrs/600 F.+4 hrs/700 F., tested at 20 Tensile Strength, psi. 1 970 1, 210 1, 540 75 F.: Elongation, percent.... 30 115 45 Tensile Strength, p.s.i 2 490 840 Hardness, Shore A, parts. 98 91 05 155 150 Aged 140 hr./600 F., Tested at 75 78 80 Tensile Strength, p.s.i 630 1, 900 Elongation, percent 40 20 131 220 Hardness, Shore A, parts 95 98 25 1 Sample broke when bent 180. 1 Broken when bent 180. 2 Sample appeared to be reverted. 2 Brittle, no test.

TABLE 4 Parts of AP Talc per 100 Parts stomor Original at 75 F.: I

Tensile Strength, p.s.i 2, 850 2, 540 2, 280 2, 400 3, 000 2, 600 Elongation, percent. 520 315 260 240 190 115 Hardness, Shore A, parts 66 71 75 84 Original at 400 F.:

Tensile Strength, p.s.i 130 380 460 610 700 610 Elongation, percent 115 100 90 75 Aged 16 hr./600 F., Tested at 75 1 Tensile Strength, p.s.i.. 1, 540 1, 640 1, 800 1, 720 2, 150 1, 960 Elongation, percent 290 240 215 195 95 Hardness, Shore A, parts- 60 70 75 79 87 Aged 72 hr./600 F., Tested at 75 F Tensile Strength, p.s.i. 1, 120 940 1, 030 1, 220 1, 1, 260 Elongation, percent. 95 85 80 50 35 Hardness, Shore A, p 70 81 82 87 90 95 TABLE 5 TABLE 2 Reinforcing Agent Reinforcing Agent Fibrous Mt. Carbon A-P Talc A-P Talc Powdered Black Wool Talc Original at 75 F.: 60 Original at 75 F.:

Tensile Strength, p.s.i 2, 2, 400 1,800 Tensile Strength, p.s.i 2, 460 1,980 2, 400 Elongation, percent.... 320 240 295 Elongation, percent.... 275 195 240 Hardness, Shore A, parts 76 75 66 Hardness, Shore A, parts- 78 78 75 Original at 400 F.: Aged 16 hr./600 F., Tested at 75 F.:

Tensile Strength, p.s.i---- 320 610 330 Tensile Strength, p.s.i 1, 080 1,250 1, 720 Elongation, percent... 110 110 170 Elongation, percent. 250 195 Aged 16 hrs at 600 F., Teste at 5 Hardness, Shore A, p 75 80 75 75 F.: Aged 2 hr./700 F., Tested at 75 Tensile Strength, p.s.i 1, 720 1, 720 1, 660 Tensile Strength, p.s.i 680 670 980 Elongation, percent 185 195 250 Elongation, percent-... 250 165 165 Hardness, Shore A, parts 78 79 75 Hardness, Shore A, parts... 72 73 80 Aged 72 hrs/600 F., Tested at Aged 4 hr./700 F., Tested at 75 75 F.: Tensile Strength, p.s.i 490 450 840 Tensile Strength, p.s.i 1, 270 1,220 1, 070 Elongation, percent.... 155 125 150 Elongation, percent 120 90 130 70 Hardness, Shore A, parts... 78 80 80 Hardness, Shore A, parts 90 87 85 Aged 8 hr./700 F., Tested at 75 F Aged 72 hrs/600 F., Tested at 400 Tensile Strength, p.s.i. l 360 350 2 780 F.: Elongation, percent. 85 85 60 Tensile Strength, p.s.i 370 Hardness, Shore A, parts 84 84 84 Elongation, percent 100 70 1 Could not test, stock too Weak.

1 Sample appeared to be reverted, broke when bent 180. 2 A smooth crust formed on the surface of the sam le.

TABLE 6 Reinforcing Agent Mt. Carbon A-P Black Wool Talc Tear Strength, 1b./in.:

I claim:

1. A reinforced fluoroelastomer of the following com- 2. A reinforced fluoroelastomer of the following composition:

Component: Parts by weight Vinylidene fluoride-perfluoroethylene copolymer 100 Acicular-platy talc 3040 Magnesium oxide 15 Alicyclic amine salt 2 References Cited UNITED STATES PATENTS 3,105,827 10/1963 Kaufman 260-41 3,157,614 11/1964 =Fischer 260-41 3,308,090 3/ 1967 Falcone et a1 260-41 3,334,063 8/1967 Berliner 260-41 OTHER REFERENCES Chem. Abstracts, vol. 60, 5718b, March 1964.

ALLAN LIEBERMAN, Primary Examiner. 

